Microstructural and Mechanical Property Analysis of High-Strength Low-Alloy Steel Tubes Fabricated Using Wire Arc-Directed Energy Deposition Technique

Wire arc-directed energy deposition advances complex part development, benefiting high-demand commercial applications, especially for parts with integrated cooling channels. Therefore, in the current study, hollow tubes with 6 mm internal diameter and 120 mm height were fabricated to analyse its mechanical properties along the build height. Various wire feed speeds and travel speeds were used for fabrication, and mechanical properties were evaluated using miniature tensile samples from the bottom, middle, and top regions of the part to determine localized strength. The results exhibited that the part fabricated at a wire feed speed and travel speed of 1.5 m/min and 60 cm/min, respectively, showed superior mechanical properties. The materials characterization reveals a grain size increase of 57% in the bottom and 116% in the middle, compared to the top section. Grain refinement in the bottom and the presence of martensitic austenitic islands in the top regions led to increases in ultimate tensile strength by 21.5% and 8.6%, respectively, compared to the middle section. The pole figure represents the strong texture in top regions consisting of equiaxed and columnar grains oriented parallel to the build direction. In addition, the remarkable reheating effects in the middle (74.4%) regions were confirmed using grain orientation spread analysis. Consequently, these effects led to the disintegration of martensitic austenitic islands into small-sized carbides, reducing the middle region’s hardness and strength. The top samples showed a significant distorted fraction (53.2%), possibly due to martensitic austenitic islands confirmed by fractography analysis, with the highest hardness of 302 ± 21 HV.

Graphical Abstract